1. Field of the Invention
This invention relates to a heat fixing member used in a heat fixing assembly which heats a sheetlike recording medium sandwichedly transported to a pressure contact nip zone formed between a heat fixing member and a pressure member and melts unfixed toner images held on the recording medium, to fix the former to the latter; and a heat fixing assembly having the heat fixing member.
2. Related Background Art
In general, in heat fixing assemblies used in electrophotographic systems, a heating roller and other roller are kept in pressure contact with each other, or a film or belt held on a pressure stay having a heating unit and a roller are kept in pressure contact with each other. Then, the heating roller, film or belt and other roller are synchronously rotated. The recording medium holding thereon the unfixed toner images is guided into the pressure contact zone and heated, where the unfixed toner images are melted and thereafter cooled and solidified, whereupon the toner images are fixed onto the recording medium.
The roller, film or belt on the side with which the unfixed toner images held on the recording medium comes into contact is called a heat fixing member, which is called a fixing roller, a fixing film, a fixing belt or so according to its form.
Such a heat fixing member is commonly provided on its inside with a heat-generating mechanism as a heat source. Then, heat is supplied from the inner surface side to heat the recording medium kept in contact with the outermost surface of the heat fixing member.
As the heat fixing member, it is often a member constituted basically of a roller-, film- or belt-shaped substrate and formed thereon a heat-resistant elastic layer in a single layer or a plurality of layers.
This elastic layer is often formed of a heat-resistant rubber material such as a silicone rubber or a fluorine rubber. Since, however, such a heat-resistant rubber material has a poor thermal conductivity, it comes resistant to heat when the heat from the heat source is transmitted to the recording medium. Accordingly, in order to make the heat-resistant rubber material improved in thermal conductivity, it is attempted to compound inorganic particles having a high thermal conductivity, such as alumina particles, zinc oxide particles and silicon carbide particles to secure heat conduction performance of the elastic layer. This is effective to a certain extent, but is insufficient in some points in order to be adaptable to high-speed processing in recording apparatus available in recent years.
Accordingly, as disclosed in Japanese Patent Application Laid-open No. 2002-268423, a method is proposed in which a silicone rubber is used as a rubber for the elastic layer of the heat fixing member, and gaseous-phase process carbon fibers are compounded thereinto in a small quantity to attempt to prevent oxidation degradation and improve thermal conductivity. As also disclosed in Japanese Patent Application Laid-open No. 2002-351243, a method is also proposed in which carbon fibers are mixed in the elastic layer to improve thermal conductivity in the lengthwise direction of the roller and improve temperature distribution in the lengthwise direction so as to obtain uniform fixed images.
However, in the method disclosed in Japanese Patent Application Laid-open No. 2002-268423, the interiors of the gaseous-phase process carbon fibers stand hollow, and hence it has been unable to secure thermal conductivity high enough to be adaptable to high-speed processing. Also, in the method disclosed in Japanese Patent Application Laid-open No. 2002-351243, the carbon fibers are oriented in the lengthwise direction with respect to the member, and hence, although the thermal conductivity in the lengthwise direction is secured, any heat flow paths for improving heat conduction properties are not formed in the thickness direction. Hence, it has still been unable to secure any sufficient thermal conductivity. As the result, in either case, the amount of heat to be imparted to the heating object (recording medium) may come insufficient at the pressure contact zone in the fixing assembly, so that the unfixed toner images are not well melted where its pressure contact zone dwell time (or simply “dwell time”) is short because of the processing made high-speed, resulting in an insufficient glossiness (or gloss) of images. There has been such a problem.
In recent years, image forming apparatus have been made high-speed and compact, where it is demanded for the heat fixing assembly to be adaptable to the dwell time having been more shortened, and for the heat fixing member it is desired to be more improved in its heat conduction from the heat source to the heating object.